A game is known in which a body of a user or a marker is photographed by a camera and an area of its image is replaced by another image to display the image on a display (see, for example, PTL 1). Also, a user interface system that receives movements of a mouth or hands photographed by a camera as an operation instruction of applications is known. In this way, a technique for photographing a real world, displaying a virtual world responsive to its movements, and performing some sort of information processing has been used in a wide range of fields from mobile terminals to leisure facilities, regardless of its scale.